Use extant data to contrast the social and cognitive development of first born children who remain only children or acquire a sibling over the first three years of life. Longitudinal and cross-sectional analyses will contrast the behaviors and cognitive levels of only and first borns at four ages; will address the impact of acquiring a sibling at two ages; and will contrast planned and unplanned children on the measures used. In addition, the decision to have a second child will be examined from the perspective of the mother's locus of control, femininity, concept of ideal family size, and quality of interaction with the first child.